Camshaft Position Actuator System Operation

Consisting of two major elements, the camshaft position actuator provides continuously variable camshaft-to-crankshaft timing (phasing) within a limited range of angular degrees. More than one camshaft position actuator may be used, depending on the number of camshafts and camshaft configuration. Camshaft actuators are designed to advance or retard camshaft timing from the base timing, depending on the application. Typically, intake cam timing is advanced, and exhaust timing is retarded to achieve desired results.

The sprocket housing is driven by the engine timing belt or chain. Inside the sprocket housing is the second element of the actuator, the rotor. Featuring three to four lobes, the rotor fits inside a similarly shaped cavity within the sprocket housing, creating oil chambers on either side of each lobe. Oil passages from the center of the camshaft provide filling or venting of the two chambers. At the center, the rotor is fastened in a fixed position to the camshaft. With no oil pressure in either chamber, a torsional spring returns the rotor to base timing.

Camshaft position actuator solenoid valves are separate, electrically actuated solenoid valve assemblies. Located away from the camshaft position actuators, they are typically installed in the camshaft cover. Oil passages through the cam cover, cylinder head, and camshaft journals hydraulically connect actuator solenoid valve oil pressure to the different actuator chambers.

Camshaft position actuator solenoid valves have three duty cycle ranges controlling the relative position between the camshaft position actuator outer sprocket and the inner rotor. From 0 to 40% duty cycle, oil is vented from apply chambers while oil pressure is applied to the opposite chambers returning camshaft timing toward base timing. At 40-55% duty cycle, the solenoid valve moves to a hold position, closing both actuator chamber passages, preventing oil flow in or out of any chambers. From 55 to 100% duty cycle, oil pressure is applied to the apply chambers, and vented from the opposite chambers, to move camshaft timing away from base timing.

During operation, the ECM may require camshaft timing to be advanced or retarded from base timing. In the event of a camshaft timing change, the ECM drives the camshaft position actuator solenoid valve duty cycle above 55%, or below 40%, for a brief time period until camshaft sensors indicate the desired timing change. Once the desired timing is achieved, the ECM returns the solenoid valve duty cycle to 40 to 55%, closing both actuator chamber passages, holding the actuator in the adjusted position.

The following table provides camshaft phase commands for common driving conditions: